There is a continuing demand for lower paraffins such as C2-4 alkanes for the production of lower olefins which are used in many industrial applications. In the processing of shale oils, oil sands and tar sands there is typically a residual stream containing compounds comprising at least two aromatic rings. These types of compounds have been subjected to hydrocracking to produce higher alkanes (e.g. C5-8 alkanes) that could be used for example to produce fuels.
U.S. Pat. No. 6,652,737 issued Nov. 25, 2003 to Touvellle et al., assigned to ExxonMobil Research and Engineering Company illustrates one current approach to treating a naphthene feed (i.e. having a large amount, preferably 75 weight % of alkanes and cycloparaffin content). The cycloparaffins are subjected to a ring opening reaction at a tertiary carbon atom. The resulting product contains a stream of light olefins (e.g. ethylene and propylene). The present invention uses a different approach. The feed comprises a higher amount of unsaturated and particularly compounds containing two or more fused aromatic rings. The compounds are partially hydrogenated to have at least one ring which is saturated and the resulting product is subjected to a ring opening and cleavage reaction to yield lower (i.e. C2-4) alkanes.
Another approach is illustrated by U.S. Pat. No. 4,956,075 issued Sep. 11, 1990 to Angevine et al., assigned to Mobil Oil Corporation. The patent teaches treating gas oil, tar sands or shale oil with an Mn catalyst on a large size zeolite support to yield a higher alkane stream suitable for use in gasoline or alkylation processes. The present invention uses a different catalyst and produces a different product stream.
The present invention seeks to provide a process for treating a feed containing significant portion (e.g. not less than 20 weight %) of aromatic compounds containing two or more fused aromatic rings. One ring is first saturated and then subjected to a ring opening and cleavage reaction to generate a product stream containing lower (C2-4) alkanes. The resulting lower alkanes may then be subjected to conventional cracking to yield olefins. In a preferred embodiment the processes are integrated so that hydrogen from the steam cracking process may be used in the saturation and ring opening steps. The process of the present invention will be particularly useful in treating heavy fractions (e.g. gas oils) from the recovery of oil from shale oils or tar sands. It is anticipated such fractions will significantly increase in volume with the increasing processing of these types of resources.